The present invention relates to texturing of magnetic data storage media, and more particularly to the texturing of dedicated transducing head contact zones of such media to minimize system resonance.
Laser texturing of magnetic disks, particularly over areas designed for contact with data transducing heads, is known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules, rather than rims. In some cases, each of the domes is surrounded by a raised rim. The features can be axisymetric, i.e. with circular profiles, or can have non-axisymetric or elliptical profiles. In the latter case, the long axes of the texturing features preferably extend circumferentially relative to the disk.
Collectively, the texturing features are formed in a desired pattern or distribution throughout the head contact zone. A particularly preferred pattern is a spiral, formed by rotating the disk at a desired angular speed while at the same time moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. For example, the disk can be rotated at a speed, variable depending on the radial position of the laser, to provide a linear (arcuate) velocity of about one meter per second. Then, operating the laser at 50,000 pulses per second would provide a 20 micron circumferential pitch, i.e. distance between adjacent texturing features. The radial speed of the laser module controls the radial pitch or spacing between adjacent turns of the spiral, which also can be about 20 microns.
Although this approach has been highly successful in terms of reducing dynamic friction and improving the wear characteristics of dedicated transducing head contact zones, the regular, repeating pattern of the laser texture features produces strong input excitations based on the fundamental frequency of the circumferential pitch, including higher order harmonics. When the excitation frequencies coincide with natural frequencies of the slider or its gimbal and support system, resonance occurs which results in a high amplitude acoustic emission signal, which can increase the difficulty of determining the glide avalanche breaking point (a disk/transducing head spacing value), and yield a false indication that the disk has failed a glide test.
Apart from their contribution to resonance, the regularly spaced apart texturing features are thought to contribute to transducing head disturbances in two further respects. First, an intermittent contact of the peaks of texturing features with the data transducing head during disk accelerations and decelerations can disturb the head. Second, the texturing features contribute to turbulence in the air bearing that supports the transducing head slider during portions of accelerations and decelerations.
Therefore, it is an object of the present invention to provide a texturing feature adapted to impart a desired surface roughness to the dedicated transducing head contact zone of a recording medium while minimizing undesirable resonant frequency effects.
Another object is to provide a magnetic data storage medium in which a head contact zone has a topography that is directionally controlled, in that surface height gradients occur primarily in the direction perpendicular to the direction of transducing head travel relative to the disk.
A further object is to provide a process for laser texturing a data storage medium to form texturizing features that are elongate and highly uniform in the direction of storage media travel.
Yet another object is to provide magnetic data storage media that exhibit the highly favorable dynamic friction and wear characteristics of laser textured media, and further exhibit low resonance interactions with transducing heads during head take-offs and landings.